1. Field of the Invention
The present invention relates to a developing apparatus which produces an electrostatic latent image, and more particularly to developing apparatus using a magnetic developer. The present invention provides a developing apparatus which is equipped with a developer quantity regulating means designed so that the magnetic developer can be uniformly and thinly supported on a developer transporting means supplying magnetic developer, which is a magnetic developer used in a one-component developing process, or supplying a magnetic carrier which is a magnetic developer used in a two-component developing process to a developing area.
2. Description of the Prior Art
In two-component developing processes which have so far been popular, they have had to use a developer comprising a toner and a carrier mixed in a certain ratio, and have replenished the toner so that the ratio mix of said toner and carrier can constantly be kept uniform in order to make an image density stable; in contrast therewith, in one-component developing process which uses a developer without a carrier and is composed of only a toner, and there is no problem with the mixing ratio, and therefore a simply constructed developing apparatus is practicable.
The toner used in a one-component developing process has to be transported to the developing area by some method or other. A toner transporting method being popularly used in the one-component developing process is that when a magnetic toner is to be used as to said toner as in the following description, as for the said developer transporting means there is arranged a non-magnetic outer cylindrical member (i.e., a sleeve) and, inside the said sleeve, a cylindrical magnetic rotating member (i.e., a rotating member having field poles alternately arranged along the direction of the rotation, and of which the same number of N- and S-poles can be arranged, for example, they are arranged in the order of S-pole, N-pole, S-pole, N-pole, . . . ; and hereinafter referred only to as magnet roll) which is co-axial with said sleeve, and said magnetic toner magnetically adheres to said sleeve by applying a magnetic field onto the outer circumferential surface of said magnet roll, and at the same time said magnetic toner is moved and transported to the developing area by the movement of the magnetic field produced by the rotation of the aforesaid magnet roll.
Such a magnetic toner contains in the grains thereof, a magnetic powder such as a magnetite, and additionally a resin, a coloring agent such as carbon black, and an electric charge controlling agent. Now in a one-component developing process, if a uniform quantity of magnetic toner is not supplied to the developing area at the place proper time and for the said supply, there results adhesion blurs of a toner (a magnetic toner) to a toner image that is the primary image on an image supporting member after the development, and in turn, there also results an unevenness of the image density of copied material, and thus the overall copying performance is seriously lowered.
Therefore, it is desired that the magnetic toner (i.e., the thickness of said toner layer) should adhere to the sleeve very uniformly. The layer of said magnetic toner requires as a condition for forming a high quality copied matter and for improving an image transfer efficiency, not only the adhesion of said layer uniformly over to said sleeve, but also the adhesion between said layers, for example, within the limits of several to tens layers in the case where the grain diameter of magnetic toner is of the order of 10.mu..
Heretofore, there have been proposed a variety of methods for forming a magnetic toner layer uniformly and thinly on the sleeve. In the early days, there has even been proposed and studied a method (i.e., a mechanical blade method) for scraping off (regulating) the magnetic toner from the sleeve mechanically by means of a plate-like member, however, in the this mechanical blade method, in order to regulate the thickness of said magnetic toner uniformly and very thinly, there were the problems that said mechanical blade member must be accurately manufactured, and that the space between the blade and the outer circumferential surface of said sleeve must be very accurately adjusted when the blade is to be fitted. Furthermore, in the said mechanical blade method, the thickness of magnetic toner actually formed varies with the grain diameter and the fluidity of said magnetic toner; however, said thickness becomes fairly greater than the space between the outer circumferential surface of said sleeve and said mechanical blade, and it was therefore very difficult to regulate the thickness of said magnetic toner to make it thinner. Still further, magnetic toner must pass through the very narrow space (the toner regulating area) between the outer circumferential surface of the sleeve and the mechanical blade that is the toner regulating member; therefore, there were some instances where strong pressure was applied adjacent the sleeve side of said mechanical blade, and said magnetic toner was forcibly cohered. Additionally, said toner regulating area becomes clogged with said cohered toner or toner cake which had been cohered by other causes, and consequently there produced, on the sleeve, an area not having adhering magnetic toner (e.g., an area where a line or a band is formed), and there was the serious danger that a white line, a white band or the like would appeared on a copy image.
Thereafter, with the purpose of making up for the defects of the developer regulating blade, there have been proposed various technologies as disclosed in Japanese Patent Publication Laid-open to Public Inspection No. 125844/1978, for example. In the drawings, FIG. 1 is a schematic diagram of the above-given described technology and the brief description thereof is as follows: Numeral 1 is a charge retaining member forming an electrostatic latent image, which rotates in the direction of the broken line and the arrow in the figure. When the layer of magnetic toner 6A is formed on the outer circumferential surface of a sleeve 3 so that magnetic toner 6 can be supplied to developing area 5, developer layer thickness regulating plate 7 comprising magnetic material is provided at the position opposite to the outer circumferential surface of sleeve 3 to regulate the layer of magnetic toner 6. The toner layer thickness regulating plate 7 is magnetically induced by a magnetic pole (i.e., N-polarity as in FIG. 1) of magnet roll 4 which is inside of sleeve 3 and is positioned opposite to the end of said layer thickness regulating plate 7, and by reason of a magnetic field generated between said regulating plate 7 being then inductively magnetized and the magnetic pole facing opposite thereto, it is difficult to pass the magnetic toner 6A through toner the regulating area 8 and as countermeasure, a developing means 2 capable of forming a layer of magnetic toner 6 thinly on sleeve 3 has been proposed. Numeral 6A shows a magnetic toner on sleeve 3 after it has passed through the toner regulation area 8. In accordance with above disclosed technology, it became possible to form a thin layer of magnetic toner more easily compared with the developer regulating means using said mechanical blade method; however, there were still some instances where the cohesion of magnetic toner occurred around the toner regulating area.